dt-bindings: mmc: Add bindings for LiteSDCard

LiteSDCard is a small footprint, configurable SDCard core for
FPGA based SoCs.
Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20220113170300.3555651-3-gsomlo@gmail.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/litex,mmc.yaml

+# SPDX-License-Identifier: GPL-2.0-or-later OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mmc/litex,mmc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: LiteX LiteSDCard device
+
+maintainers:
+  - Gabriel Somlo <gsomlo@gmail.com>
+
+description: |
+  LiteSDCard is a small footprint, configurable SDCard core for FPGA based
+  system on chips.
+
+  The hardware source is Open Source and can be found on at
+  https://github.com/enjoy-digital/litesdcard/.
+
+allOf:
+  - $ref: mmc-controller.yaml#
+
+properties:
+  compatible:
+    const: litex,mmc
+
+  reg:
+    items:
+      - description: PHY registers
+      - description: CORE registers
+      - description: DMA Reader buffer
+      - description: DMA Writer buffer
+      - description: IRQ registers
+    minItems: 4
+
+  reg-names:
+    items:
+      - const: phy
+      - const: core
+      - const: reader
+      - const: writer
+      - const: irq
+    minItems: 4
+
+  clocks:
+    maxItems: 1
+    description:
+      Handle to reference clock.
+
+  vmmc-supply:
+    description:
+      Handle to fixed-voltage supply for the card power.
+
+  interrupts:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - reg-names
+  - clocks
+  - vmmc-supply
+
+additionalProperties: false
+
+examples:
+  - |
+    mmc: mmc@12005000 {
+        compatible = "litex,mmc";
+        reg = <0x12005000 0x100>,
+              <0x12003800 0x100>,
+              <0x12003000 0x100>,
+              <0x12004800 0x100>,
+              <0x12004000 0x100>;
+        reg-names = "phy", "core", "reader", "writer", "irq";
+        clocks = <&reference_clk>;
+        vmmc-supply = <&vreg_mmc>;
+        interrupts = <4>;
+    };